My Dog Is Eating Extremely Slow, Not Acting Herself, And Is Very Slow At Walking Up And Down The Stairs?

Your dog showing the symptoms of lethargy. This is a condition in dogs which is identified by late responses to the external stimuli. This condition should not be ignored in dogs especially if continues for more than 24 hours. This can be due to any disease or condition. Most common causes of lethargy in dogs are

1. Electrolyte imbalance
2. Anemia
3. Cardiovascular disorders
4. Infections
5. Hormonal disorders
6. Cancer
7. Skin diseases
8. Eye diseases
9. Toxic reactions
10. Side effects of medicines
11. Immune diseases

So, only vet can diagnose properly. In my opinion, get advice from your vet by visiting him.